Semiconductor integrated circuit device

ABSTRACT

A semiconductor integrated circuit device has a data storage section for storing mode setting data corresponding to products of a plurality of types, redundancy data, and so on. The redundancy storage section is made up of a nonvolatile transistor for storing the mode setting data corresponding to the products, the redundancy data, etc., a latch circuit for latching data read out from the nonvolatile transistor and generating a mode signal, and a transmission gate for transmitting the data from read out from the nonvolatile transistor to the latch circuit. The semiconductor integrated circuit device also has an internal voltage generator for generating an internal voltage. This internal voltage is used as the power supply voltage of the data storage section.

This application is a divisional of prior application Ser. No.09/030,915 filed Feb. 26, 1998, now U.S. Pat. No. 6,052,313.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice which comprises a data storage section, formed inside a chip, forstoring desirable mode setting data corresponding to products of aplurality of types, redundancy data, and so on.

Examples of product types in a semiconductor integrated circuit deviceare

(1) a product type in which the layout of pads depends on a package suchas TSOP (Thin Small Outline Package)/SOP (Small Outline Package), andthe locations of pads to be used are switched,

(2) a product type in which parallel data have different bit lengthssuch as ×4, ×8, and ×16, and the numbers of I/O blocks and senseamplifiers to be activated change in accordance with a bit length, and

(3) a product type in which addressing changes such that the top andbottom of an address for designating an irregular block are switched inan irregular-block product in a flash EEPROM.

In the semiconductor integrated circuit device having a plurality ofdifferent modes, the operation mode of the device must be determined bysome method.

In general, either of the master slice or bonding option methods isconventionally selected in order to develop one mask set into the typesof products having a plurality of different modes.

In the master slice method, different modes are switched by exchanging,e.g., Al masks. This method is generally used in developing one mask setinto a plurality of mode types.

On the other hand, the bonding option method uses an input signal from adummy pad to select a different mode. A power supply voltage or groundpotential is applied to the dummy pad to determine the mode of anintegrated circuit by either potential.

A semiconductor integrated circuit device in which a plurality ofproduct types are developed by the bonding option method is disclosedin, e.g., the following reference:

EUROPEAN PATENT Publication Number 0 476 282 A2 (lines 29-44, p. 10,FIG. 1n and the like).

In the bonding option method, no plurality of masks need be preparedcompared to the master slice method, and data need not be managed incorrecting the mask.

In the master slice method, one product type requires one mask. Assumethat four product types are simultaneously developed, and the producttype is switched by Al masks. If a given Al mask must be corrected, fourAl masks must be corrected, resulting in high mask cost. If the numberof times of correction is large, the correction contents may not becompletely managed. All functions corresponding to the corrected masksmust be checked, and the evaluation is cumbersome.

In the bonding option method, a power supply or ground potential isapplied to a dummy pad for determining the contents of a device.Therefore, the dummy pad must be arranged between power supply pins orground pins. Alternatively, the bonding option exclusively requires apad connected to the power supply and a pad connected to the groundadjacent to the dummy pad. Since the bonding option method requires alarge number of extra pads to lead to an increase in chip area, thismethod cannot cope with so many modes.

Semiconductor integrated circuit devices designed in consideration ofthe above technology and comprising data storage sections that storemode setting data corresponding to products of a plurality of types, aredisclosed, for example, in the following publications:

Jpn. Pat. Appln. KOKAI Publication No. 2-116084 (the description betweenthe fourteenth line of the lower left column of page 2 and the eleventhline of the lower right column of the same page, and FIG. 2); and

Jpn. Pat. Appln. KOKAI Publication No. 6-243677 (the descriptions inparagraphs [0044] and [0102], and FIG. 10)

In the semiconductor integrated circuit device disclosed in each ofthese publications, mode setting data are stored in a nonvolatiletransistor. Due to this feature, the semiconductor integrated circuitdevice enables one mask set to be developed into a plurality of producttypes, eliminates the need for extra pads, and does not thereforerequire an increased chip area.

The data storage section, which includes a nonvolatile transistor,stores mode setting data corresponding to products of a-plurality oftypes. Accordingly, the data storage section requires very highreliability.

However, the two Japanese KOKAI publication No. 2-116084 and No.6-243677 do not disclose any measures that can be taken to improve thereliability of the data storage section.

BRIEF SUMMARY OF THE INVENTION

It is the first object of the present invention to increase thereliability of a data memory portion for storing, for example, desiredmode setting data corresponding to a plurality of product types to datamemory portion being arranged with a chip.

To achieve the first object, according to the present invention, aninternal power supply generated within the chip is used as the powersupply of the data memory portion instead of an external power supply.

More specifically, in the present invention, by using the internal powersupply generated within the chip as the power supply of the data memoryportion, a malfunction of the data memory portion caused by, e.g.,fluctuations in voltage of the external power supply is prevented.

To further suppress an increase in chip area, the data memory portionrequires the same micro-lithography technique as that applied to anotherintegrated circuit portion formed within the same chip. For example, inthe data memory portion, a power supply voltage must be decreased.

However, if the power supply voltage is decreased, data may not becorrectly read out from the data memory portion. The data memory portionstores, for example, desired mode setting data corresponding to aplurality of product types to determine the type of product. For thisreason, high precision is required for the reading of data from the datamemory portion.

It is the second object of the present invention to read out data fromthe data memory portion at high precision even if the power supplyvoltage is decreased.

To achieve the second object, according to the present invention, datais read out from the data memory portion at a boosted voltage higherthan the power supply voltage.

That is, in the present invention, data is read out from the data memoryportion at the boosted voltage higher than the power supply voltage.With this setting, even if the data memory portion stores data using anonvolatile memory cell, the data read precision is increased byincreasing the difference between the threshold voltage of thenonvolatile memory cell in an “ON” state, and the voltage of the controlgate.

When the power supply voltage becomes low, it may happen that theinternal power supply voltage is not high enough to operate the datastorage section in a reliable manner, particularly when the system isturned on. The data storage section stores desirable mode setting datacorresponding to products of a plurality of types, and the type of aproduct is determined on the basis of the mode setting data. Therefore,the data storage section must be operated as soon as the system isturned on. The data storage section must be reliably operated even whenthe internal power supply voltage is not very high, such as the timewhen the system has just been turned on.

It is the third object of the present invention to correctly operate thedata memory portion upon, particularly, power-on.

To achieve the third object, in the present invention, a circuit fordetecting the voltage of the internal power supply and outputting asignal representing that the voltage of the internal power supplyincreases to a voltage high enough to correctly operate the data memoryportion is arranged within the chip. The operation of the data memoryportion is enabled by a signal from this circuit.

In other words, in the present invention, the data memory portion isoperated only when the voltage of the internal power supply increases toa voltage high enough to correctly operate the data memory portion. As aresult, the data memory portion correctly operates upon, particularly,power-on.

The data memory portion stores, for example, desired mode setting datacorresponding to a plurality of product types. Therefore, the datamemory portion must have high reliability and good durability. When thedata memory portion is mounted on a semiconductor memory device chip,its durability must be equal to or higher than that of a memory cellarray.

It is the fourth object of the present invention to increase thedurability of the data memory portion.

To achieve the fourth object, in the first embodiment of the presentinvention, the data memory portion comprises a nonvolatile memory cellfor storing, for example, mode setting data, a latch circuit forlatching the data of the nonvolatile memory cell and outputting, forexample, a mode signal, and a switch for connecting the latch circuitand the nonvolatile memory cell to each other in reading out, forexample, the mode setting data from the nonvolatile memory cell, anddisconnecting the latch circuit from the nonvolatile memory cell after,for example, the mode setting data is latched by the latch circuit.

More specifically, in the present invention, after, for example, themode setting data read out from the nonvolatile memory cell is latchedby the latch circuit, the latch circuit and the nonvolatile memory cellare disconnected from each other by the switch to suppress an electricalstress applied to the nonvolatile memory cell. This arrangementincreases the durability of the data memory portion.

If a voltage between the gate of the nonvolatile memory cell and asubstrate, and a voltage between the source and drain are decreased, anelectrical stress applied to the nonvolatile memory cell is furthersuppressed.

When the data memory portion is constituted including the nonvolatilememory cell, the data memory portion requires the same micro-lithographytechnique as that applied to the memory cell array of a nonvolatilesemiconductor memory device in order to further suppress an increase inchip area.

It is the fifth object of the present invention to micro-pattern thedata memory portion constituted including the nonvolatile memory cell.

To achieve the fifth object, according to the present invention, anarray in which nonvolatile memory cells are arranged is formed andsandwiched between arrays in which dummy nonvolatile memory cells arearranged.

More specifically, in the present invention, by sandwiching the array inwhich the nonvolatile memory cells are arranged between the arrays inwhich the dummy nonvolatile memory cells are arranged, the array havingthe nonvolatile memory cells can be prevented from being an isolatedpattern on the chip. Accordingly, the data memory portion constitutedusing the nonvolatile memory cell can be formed by the most advancedmicro-lithography capable of forming a finer pattern as an interferencephenomenon of light becomes more conspicuous.

In the data memory portion, various data including defective addressdata, and redundancy data such as data for activating a spare decoder(to be described later) can be stored in addition to desired modesetting data corresponding to a plurality of product types. Additionalobjects and advantages of the invention will be set forth in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram showing the arrangement of a chip when thepresent invention is applied to a nonvolatile semiconductor memory;

FIG. 2 is a circuit diagram of a mode signal generator;

FIG. 3 is a circuit diagram of a sense amplifier circuit and an I/Obuffer;

FIG. 4 is a circuit diagram of a circuit for generating signals Add and/Add;

FIG. 5 is a table showing the potential relationship in a write, erase,and read with respect to a nonvolatile transistor; FIG. 6A is aconceptual view in writing data in the nonvolatile transistor; FIG. 6Bis a conceptual view in erasing data from the nonvolatile transistor;

FIG. 7 is a block diagram showing the arrangement of a semiconductorintegrated circuit device according to the first embodiment of thepresent invention;

FIG. 8A is a circuit diagram of a memory cell array;

FIG. 8B is a sectional view of a memory cell;

FIG. 8C is a symbol diagram of the memory cell;

FIG. 8D is an equivalent circuit diagram of the memory cell;

FIG. 9 is a block diagram showing the arrangement of a semiconductorintegrated circuit device according to the second embodiment of thepresent invention;

FIG. 10 is a block diagram showing the arrangement of a semiconductorintegrated circuit device according to the third embodiment of thepresent invention;

FIG. 11 is a flow chart showing the control sequence of a flash EEPROMaccording to the fourth embodiment of the present invention;

FIG. 12 is a block diagram of the arrangement of the flash EEPROMaccording to the fourth embodiment of the present invention;

FIG. 13 is a circuit diagram of a power-on reset circuit;

FIG. 14 is a circuit diagram of a reference voltage generator;

FIG. 15 is a circuit diagram of a timing adjuster;

FIG. 16 is a circuit diagram of an oscillator;

FIG. 17 is a circuit diagram of a charge pumping circuit;

FIG. 18 is a circuit diagram of a VDDR level detector;

FIG. 19 is a circuit diagram of a latch circuit;

FIG. 20 is a circuit diagram of a fuse cell data latch trigger circuit;

FIG. 21 is a circuit diagram of a fuse cell control circuit;

FIG. 22 is a circuit diagram of a fuse cell;

FIG. 23 is a circuit diagram of a fuse cell data latch circuit;

FIG. 24 is a waveform chart showing the operation of a data read/latchsequence;

FIG. 25 is a circuit diagram of a fuse cell data latch trigger circuitaccording to the fifth embodiment of the present invention;

FIG. 26 is a waveform chart showing the operation of a data read/latchsequence according to the fifth embodiment of the present invention;

FIG. 27A is a view showing the layout of flash EEPROMs on a circuitboard according to the fifth embodiment of the present invention;

FIG. 27B is a circuit diagram of an internal chip enable signal outputcircuit;

FIG. 28 is a circuit diagram of a fuse cell data latch trigger circuitaccording to the sixth embodiment of the present invention;

FIG. 29 is a plan view of the pattern of a fuse cell array according tothe seventh embodiment of the present invention;

FIG. 30 is an equivalent circuit diagram of the fuse cell arrayaccording to the seventh embodiment of the present invention;

FIG. 31 is an equivalent circuit diagram of a fuse cell array accordingto the eighth embodiment of the present invention;

FIG. 32 is a block diagram showing an example of the arrangement of aflash EEPROM according to the ninth embodiment of the present invention;and

FIG. 33 is a view showing the relationship between the fuse cell arrayof a flash EEPROM according to the tenth embodiment of the presentinvention, and a main memory cell array.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the several views of the accompanying drawing.

First Embodiment

FIG. 1 is a block diagram showing an example of the internal arrangementof a chip when the present invention is applied to a nonvolatilesemiconductor memory.

In FIG. 1, a memory cell array 11 comprises pluralities of bit lines BLand word lines WL (only one bit line BL and one word line WL are shown),and a plurality of memory cells (flash cells; only one of them is shown)MC, each of which has a floating gate, a control gate, and a source anddrain, and in which data is programmed (written) upon a change inthreshold voltage viewed from the control gate by injecting electronsinto the floating gate, and data is electrically erased. The controlgate of each memory cell MC is connected to one of the plurality of wordlines WL, and its drain is connected to one of the plurality of bitlines BL. The source of each memory cell MC is connected to a commonsource line (not shown) in units of bit lines, word lines, or blocks.

An address buffer 12 receives an external address signal to generate aninternal address signal. The internal address signal generated by theaddress buffer 12 is supplied to a row decoder 13, a column decoder 14,a source decoder 15, and a mode signal generator 16.

An I/O control circuit 17 receives a chip enable signal /CE, a writeenable signal /WE, and an output enable signal /OE which are externallyinput, and generates various control signals for controlling theoperations of internal circuits on the basis of these input signals. Forexample, a control signal based on the chip enable signal /CE issupplied to the address buffer 12, which is allowed to generate aninternal address signal on the basis of this control signal. A controlsignal based on the output enable signal /OE is supplied to an I/Obuffer (to be described later), which is allowed to output data on thebasis of this control signal. A control signal based on the write enablesignal /WE is supplied to a write circuit (to be described later), whichis allowed to write data on the basis of this control signal.

The row decoder 13 selects a word line WL in the memory cell array 11 onthe basis of the internal address signal (internal row address signal).

A column selector 18 selects a bit line BL in the memory cell array 11on the basis of a decoded output from the column decoder 14.

The source decoder 15 selects a source line in the memory cell array 11on the basis of the internal address signal, and applies a predeterminedvoltage to the selected source line.

In writing data, a write circuit 19 supplies write data to a selectedmemory cell in the memory cell array 11 to write the data.

In reading out data, a sense amplifier (S/A) 20 senses data read outfrom a selected memory cell in the memory cell array 11.

An I/O buffer 21 sends externally supplied data to the write circuit 19in writing data, and externally outputs data sensed by the senseamplifier (S/A) 20 in reading out data. The I/O buffer 21 receivescommand data for setting various operation modes, i.e., data write,erase, and read modes, and a product mode in developing the types ofmode products.

The I/O buffer 21 is connected to a command/user interface circuit 22. Acontrol signal output from the I/O control circuit 17 is also input tothe command/user interface circuit 22. At a timing when the write enablesignal /WE is activated, the command/user interface circuit 22 receivescommand data input through the I/O buffer 21. An output from thecommand/user interface circuit 22 is supplied to an internal controlcircuit 23. The internal control circuit 23 generates an internalcontrol signal in accordance with the command data received by thecommand/user interface circuit 22. This internal control signal issupplied to an internal power supply/booster 24.

The internal power supply/booster 24 receives an external voltage, andgenerates an internal voltage from the external voltage, or a boostedvoltage using a charge pump on the basis of the internal control signal.The internal voltage/boosted voltage generated by the internal powersupply/booster 24 is distributed to each circuit on the same chip.

The mode signal generator 16 comprises a plurality of nonvolatiletransistors, each of which has floating and control gates, and in whichdata is programmed upon a change in threshold voltage viewed from thecontrol gate by injecting electrons into the floating gate, and data iselectrically erased, similar to the memory cell. Mode setting data iswritten in each nonvolatile transistor of the mode signal generator 16in a wafer state upon completion of processing in a clean room generallycalled postprocessing, or in a step upon assembling. Examples of thismode setting data are

(1) data used when the layout of pads depends on a package such asTSOP/SOP, and the locations of pads to be used are switched,

(2) data used when parallel data have different bit lengths such as ×4,×8, and ×16, and the numbers of I/O blocks and sense amplifiers to beactivated change in accordance with a bit length, and

(3) data used when addressing changes such that the top and bottom of anaddress for designating an irregular block are switched in anirregular-block product in a flash EEPROM. The mode signal generator 16reads out mode setting data stored in the nonvolatile transistors at apredetermined timing, and generates a mode signal on the basis of theread data. The generated mode signal is supplied to, e.g., the I/Obuffer 21.

FIG. 2 shows a detailed circuit arrangement of a part related to thenonvolatile transistor storing one mode setting data in the mode signalgenerator 16 in FIG. 1.

As shown in FIG. 2, in a nonvolatile transistor 31 having floating andcontrol gates, data is programmed upon a change in threshold voltageviewed from the control gate by injecting electrons into the floatinggate. The source of the nonvolatile transistor 31 is grounded, and itsdrain is coupled to a node 33 via an N-channel MOS transistor 32. Thecontrol gate of the nonvolatile transistor 31 and the gate of thetransistor 32 are commonly connected. The common gate receives a controlsignal PWON which changes to “H”level within a predetermined periodafter the power supply voltage is supplied to the whole chip. A circuitfor generating the control signal PWON is a well-known power-on clearsignal generator or the like, and a detailed description thereof will beomitted.

A load element 34 made up of, e.g., a P-channel MOS transistor isconnected between the node 33 and the power supply voltage. One terminalof a CMOS transmission gate 37 made up of an N-channel MOS transistor 35and a P-channel MOS transistor 36 is connected to the node 33. Thecontrol signal PWON is supplied to the gate of the N-channel MOStransistor 35, whereas a control signal /PWON complementary in level tothe signal PWON is supplied to the gate of the P-channel MOS transistor36. The other terminal of the transmission gate 37 is connected to oneterminal of a latch circuit 40 made up of two inverters 38 and 39 havingI/O terminals reversely parallel-connected to each other. A signal fromthe other terminal of the latch circuit 40 is input to an inverter 41,and an output signal from the inverter 41 is supplied as a mode signalMODE to the I/O buffer 21.

FIG. 3 shows the arrangement of part of the sense amplifier 20 and theI/O buffer 21 when the I/O buffer 21 in FIG. 1 can select either mode“x1” or mode “x2”in reading out data. FIG. 4 shows a circuit forgenerating signals Add and /Add used in FIG. 3.

In FIG. 3, reference symbols S/A11 and S/A12 denote sense amplifierseach arranged in the sense amplifier 20 to sense 1-bit data. Referencenumerals 51 and 52 denote output buffers each for outputting 1-bit data.Each of the output buffers 51 and 52 is constituted by a P-channel MOStransistor 53 having a source connected to the power supply voltage, andan N-channel MOS transistor 54 having a drain connected to the drain ofthe transistor 53 and a grounded source. Each of output pads OUT1 andOUT2 is connected to the common drain of the transistors 53 and 54 ineach of the output buffers 51 and 52.

An output from one sense amplifier S/A11 is supplied to one outputbuffer 51 via an N-channel MOS transistor 56 and an interver 57. Anoutput from the other sense amplifier S/A12 is supplied to one inputterminal of a NAND gate 58. An output from the NAND gate 58 is suppliedto the other output buffer 52. An N-channel MOS transistor 59 isconnected between the input terminal of the interver 57 and one inputterminal of the NAND gate 58. The other input terminal of the NAND gate58 receives the mode signal MODE generated by the circuit in FIG. 2. Thegate of the transistor 56 receives the address signal Add, while thegate of the transistor 59 receives the address signal /Add complementaryin level to the address signal Add.

FIG. 4 shows a detailed arrangement of a circuit portion for generatingthe complementary address signals Add and /Add used in the circuit ofFIG. 3. In this circuit, a 1-bit internal address signal AddIN generatedby the address buffer 12 (shown in FIG. 1) is supplied to one inputterminal of a NOR gate 61. The mode signal MODE is supplied to the otherinput terminal of the NOR gate 61. An output from the NOR gate 61 issupplied to an inverter 62, and an output from the inverter 62 issupplied as the signal Add to the gate of the transistor 56 in FIG. 3.The output from the inverter 62 is further supplied to an inverter 63,and an output from the inverter 63 is supplied as the signal /Add to thegate of the transistor 59 in FIG. 3.

The circuit shown in FIG. 4 is arranged in the mode signal generator 16in the first embodiment, but may be arranged outside the mode signalgenerator 16 or in another circuit.

Nonvolatile semiconductor memory chips each having the respectivecircuits are simultaneously manufactured using completely the same maskset regardless of different mode types wherein I/O buffers 21 read outdata in modes “x1” and “x2”. In a wafer state upon completion ofprocessing in a clean room called postprocessing, or in a step uponassembling, mode setting data is written in the nonvolatile transistor31 in the circuit of FIG. 2. For example, in the first embodiment,electrons are injected into the floating gate in order to set thenonvolatile transistor in mode “x2”, whereas no electron is injected inorder to set it in mode “x1”.

When the user uses a nonvolatile semiconductor memory chip programmed inthis manner upon incorporating it in a system, if the power supplyvoltage is applied to the chip, the control signal PWON changes to “H”level within a predetermined period to turn on the transistor 32 in FIG.2 and read out memory data from the nonvolatile transistor 31 to thenode 33.

When data corresponding to mode “x2” in which electrons are injectedinto the floating gate in advance is stored in the nonvolatiletransistor 31, the nonvolatile transistor 31 is not turned on becauseits threshold voltage has gone high. Therefore, the node 33 changes to“H” level. Since the control signal /PWON is at “L” level for an“H”-level control signal PWON, the transmission gate 37 in FIG. 2 isturned on to transmit the “H”-level signal of the node 33 to the latchcircuit 40. After the control signals PWON and /PWON respectively returnto “L” level and “H”-level, the latch circuit 40 holds this state. Thatis, in mode “x2”, the circuit in FIG. 2 outputs an “H”-level mode signalMODE.

When data corresponding to mode “x1” in which no electron is injectedinto the floating gate is stored in the nonvolatile transistor 31, itsthreshold voltage remains low. If the “H”-level control signal PWON issupplied to the control gate, the nonvolatile transistor 31 is turnedon. Accordingly, the node 33 changes to “L” level. That is, in mode“x1”, the circuit in FIG. 2 outputs an “L”-level mode signal MODE.

In the circuit of FIG. 3, in mode “x2”, the NAND gate 58 operates as aninverter because the mode signal MODE is at “H” level. At this time,since the signal Add supplied the gate of the transistor 56 is at “H”level, and the signal /Add supplied to the gate of the transistor 59 isat “L” level, the transistor 56 is turned on, and the transistor 59 isturned off. As a result, data sensed by the two sense amplifiers S/A11and S/A12 are output parallel from the output pads OUT1 and OUT2 via theoutput buffers 51 and 52.

In mode “x1”, since the mode signal MODE is at “L” level, an output fromthe NAND gate 58 is always at “H” level regardless of an output from thesense amplifier S/A12. Both the P-channel MOS transistor 53 and theN-channel MOS transistor 54 in the output buffer 52 are kept off, andthe output pad OUT2 is in a highimpedance state.

In accordance with an input address at that time, either one of thesignals Add and /Add changes to “H” level, and the other to “L” level.If Add=“H” level and /Add=“L” level, the transistor 56 is turned on, anddata sensed by the sense amplifier S/A11 is output from the output padOUT1 via the output buffer 51. If Add=“L” level and /Add=“H” level, thetransistor 59 is turned on, and data sensed by the sense amplifier S/A12is output from the output pad OUT1 via the output buffer 51. That is, inmode “x1”, 2-bit data sensed by the sense amplifiers S/A11 and S/A12 areoutput from one output pad OUT1 in accordance with an address state atthat time.

In the circuit of FIG. 4, in mode “x2”, since the mode signal MODE is at“H” level, an output from the NOR gate 61 is at “L” level regardless ofthe input address signal AddIN, and the signals Add and /Add arerespectively at “H” level and “L” level, as described above. In mode“x1”, since the mode signal MODE is at “L” level, an output from the NORgate 61 changes in accordance with the input address signal AddIN. Theoutput changes to “H” level for an “L”-level input address signal AddIN,and to “L” level for an “H”-level input address signal AddIN. Thesignals Add and /Add change depending on the input address signal AddIN.

In this way, a nonvolatile memory element is arranged within a chip,data about a mode of the integrated circuit is written in thenonvolatile memory element in postprocessing, and this memory data isread out to generate a mode signal. With this arrangement, theconventional problems of cumbersome management of many masks and anincrease in chip area can be solved. In addition, the mode of theintegrated circuit can be switched by rewriting the data of thenonvolatile memory element even upon completion of assembling.Accordingly, the manufacturing efficiency greatly increases because theintegrated circuit manufacturer can make production scheduling withoutconsidering the final number of products for each mode, and cansimultaneously manufacture a plurality of products having differentmodes up to an assembling step.

The description does not exemplify any detailed arrangement forprogramming/erasing data in/from the nonvolatile transistor.Programming/erase of data in from the nonvolatile transistor is the sameas programming/erase of data in/from the memory cell arranged in thememory cell array 11. FIG. 5 summarizes the respective potentialrelationships of the control gate (Vg), drain (Vd), and source (Vs) ofthe nonvolatile transistor in a write (electron injection), an erase(electron discharge), and a read.

FIG. 6A is a conceptual view in writing data in the nonvolatiletransistor. A booster 71 boosts an external voltage to generate aplurality of voltages higher than the power supply voltage. As describedabove, the mode signal generator 16 in FIG. 1 comprises a plurality ofnonvolatile transistors in order to make setting of a plurality ofdifferent modes possible. Selecting some of these nonvolatiletransistors to write data requires a selecting transistor. Thisselecting transistor is a transistor 72 in FIG. 6A. More specifically,one of the boosted voltages generated by the booster 71 is applied tothe drain of the nonvolatile transistor 31 via the transistor 72. Theremaining boosted voltages generated by the booster 71 are supplied tolevel shifters 73 and 74. Each of the level shifters 73 and 74level-shifts an “H”-level write signal to a voltage higher than thepower supply voltage. Outputs from the two level shifters 73 and 74 arerespectively supplied to the gate of the selecting transistor 72 and thecontrol gate of the nonvolatile transistor 31.

In this arrangement, to write data in the nonvolatile transistor 31, 10V (Vg) and 6 V (Vd) are respectively applied to the control gate and thedrain. Note that the source is at 0 V (Vs) because it is grounded.

FIG. 6B is a conceptual view in erasing data from the nonvolatiletransistor. A negative-voltage generator 75 generates a voltage having anegative value lower than the ground voltage of 0 V. A booster 76 boostsan external voltage to generate a voltage higher than the power supplyvoltage. The boosted voltage generated by the booster 76 is applied tothe source of the nonvolatile transistor 31. An output from thenegative-voltage generator 75 is supplied to the control gate of thenonvolatile transistor 31.

In this arrangement, to erase data from the nonvolatile transistor 31,−7 V (Vg) and 6 V (Vs) are respectively applied to the control gate andthe source. Note that the drain is open.

In the description, the difference in bit arrangement in reading outdata is described as an example of different modes. However, the exampleof different modes is not limited to the difference in bit arrangement.For example, when designation of a pad to be used (bonded) depends ondifferent packages, the mode signal is used

(1) to activate a circuit connected to the pad to be used, and

(2) to ground pads not to be used and inactivate circuits connected tothese pads.

The present invention can also be practiced in changing designation ofthe range of an operating voltage. More specifically, to operate asingle integrated circuit at, e.g., 3 V and 5 V, setting of internaltimings, the size ratios of various ratio circuits (particularlyinterfaces), and the like must be separately finely adjusted. They canbe switched and controlled using the mode signals.

The present invention can also be applied for switching control ofhigh-speed and largepower-consumption version/low-speed andsmall-power-consumption version, or control of a circuit for invertingan address input midway in order to switch the top/bottom boot of amemory block in a NOR flash memory.

The present invention is also applicable to a redundancy technique for asemiconductor memory device such as a flash memory. That is, redundancydata such as defective address data or data for activating a sparedecoder can be stored in the nonvolatile transistor 31.

Various applications of the present invention are conceivable. Thepresent invention can be applied to all cases as far as a plurality ofdifferent modes can be expressed by circuits with one internal modesignal or a combination of a plurality of internal mode signals.

In the first embodiment, mode setting data and redundancy data arestored in the nonvolatile transistor 31. The mode-signal generator 16including the nonvolatile transistor 31 generates a mode signal fordetermining a product type in accordance with the mode setting data, ora redundancy signal for replacing a defective address with a spare inaccordance with the redundancy data.

For this reason, the mode signal generator 16 must have highreliability.

FIG. 7 is a block diagram showing an example of the arrangement of asemiconductor integrated circuit device according to the firstembodiment.

As shown in FIG. 7, an internal voltage VDD boosted higher than anexternal voltage or regulated equal to/lower than the external voltageby an internal voltage generator 80 is used as the power supply of amode signal generator 16. The internal voltage generator 80 generatesthe internal voltage VDD from, e.g., the external voltage VCC.

In this manner, the power supply of the mode signal generator 16 ischanged from the external voltage VCC to the power supply terminal VDD.This can suppress any malfunction caused by fluctuations in the externalvoltage VCC or the like. As a result, the reliability of the mode signalgenerator 16 increases.

Second Embodiment

In a circuit having many analog elements, e.g., a circuit wherein datais read out from a nonvolatile transistor 31, the power supply margin isoften smaller than that of a general CMOS logic circuit.

Particularly when the internal voltage VDD shown in FIG. 7 is decreasedto encourage micropatterning of a device, the circuit having many analogelements becomes short of the power supply margin. This will beexplained by exemplifying the memory cell MC of the flash EEPROM shownin FIG. 1.

FIG. 8A is a circuit diagram of a memory cell array 11. FIG. 8B is asectional view of a memory cell MC. FIG. 8C is a circuit diagram showingsymbols in the memory cell MC. FIG. 8D is an equivalent circuit diagramof the memory cell MC.

Data is written/erased in/from the memory cell MC byinjecting/discharging electrons into/from a floating gate FG.

While electrons exist in the floating gate FG, the threshold voltageVthcell viewed from a control gate CG is high, and the memory cell MC isin an “OFF” state.

If no electron exists, the threshold voltage Vthcell viewed from thecontrol gate CG is low, and the memory cell MC is in an “ON” state. Thethreshold voltage Vthcell in an “ON” state is generally about 2 V.

The power supply voltage of a conventional flash EEPROM is generally 5V, which is directly applied to the control gate CG in a read. The cellcurrent Icell is proportional to Vd−(1/2)·Vd² (the voltage Vd is a drainvoltage and holds Vd=Vg−Vthcell for an N-channel memory cell MC, and thevoltage Vg is a control gate voltage).

When the memory cell MC is of an N-channel type, the threshold voltageVthcell is 2 V, and the control gate voltage Vg is 5 V, the drainvoltage Vd is 3 V (=Vg−Vthcell), and a satisfactory cell current Icellcan be obtained.

However, if the external power supply voltage VCC or the internal powersupply voltage VDD is lowered to 3 V or so and this lowered power supplyvoltage is applied directly to the control gate of a memory cell at thetime of reading, the voltage Vg at the control gate is 3 V, and voltageVd at the drain is 1 V (=Vg −Vthcell). For this reason, no satisfactorycell current Icell can be obtained.

When the signal PWON changes to “H” level in the mode signal generator16 shown in FIG. 2, latch data of the latch circuit 40 is determined bythe current ratio of the load 34 to the nonvolatile transistor 31.

In the circuit shown in FIG. 2, the signal PWON having the amplitude ofthe power supply voltage is supplied to the control gate of thenonvolatile transistor 31. This technique is effective when the powersupply voltage and the threshold voltage Vthcell of the nonvolatiletransistor 31 in an “ON” state have a sufficient difference.

When the power supply voltage is decreased to shorten the differencebetween the power supply voltage and the threshold voltage Vthcell ofthe nonvolatile transistor 31, the same phenomenon as that describedwith reference to FIGS. 8A to 8D occurs, and the cell current runsshort.

If the power supply voltage fluctuates in the case of a small differencebetween the power supply voltage and the threshold voltage Vthcell, thenonvolatile transistor 31 in an “ON” state may be turned off, and themode signal generator 16 may output an erroneous mode signal MODE. Ifthe erroneous mode signal MODE is output, the type of produce changes.

To eliminate such an error, e.g., the power supply margin is settighter.

However, setting a tight power supply margin may undesirably lead to adecrease in manufacturing yield and the like.

An object of the second embodiment is therefore to maintain satisfactoryreliability of a mode signal generator 16 without decreasing, e.g., themanufacturing yield even if the difference between the power supplyvoltage and the threshold voltage Vthcell of a nonvolatile transistor 31in an “ON” state becomes smaller.

FIG. 9 is a block diagram showing an example of the arrangement of asemiconductor integrated circuit device according to the secondembodiment.

As shown in FIG. 9, in the second embodiment, an internal voltagebooster 81 for boosting the internal voltage VDD to a boosted voltageVDDR is arranged within a chip. The boosted voltage VDDR is applied to acontroller 82 together with the internal voltage VDD. The controller 82outputs a signal FSWL to be supplied to the control gate of thenonvolatile transistor 31 and a signal FSBIAS to be supplied to the gateof a transistor 32 or the like in accordance with a signal PWON. Thesignal FSBIAS has the amplitude of the internal voltage VDD, and thesignal FSWL has the amplitude of the boosted voltage VDDR.

In this manner, the signal FSWL to be supplied to the control gate ofthe nonvolatile transistor 31 is set to have the boosted voltage VDDRhigher than the internal voltage VDD. This setting can increase thedifference between the power supply voltage and the threshold voltageVthcell of the nonvolatile transistor 31 in an “ON” state. Even if theinternal voltage VDD slightly fluctuates, the nonvolatile transistor 31in an “ON” state can be prevented from being turned off.

The second embodiment adopts the internal voltage VDD, but may use theexternal voltage VCC in place of the internal voltage VDD. In this case,the boosted voltage VDDR is obtained by boosting the external voltageVCC.

An example of the voltage of the signal FSBIAS is about 3 V, and anexample of the voltage of the signal FSWL is about 5 V. That is, in thethird embodiment, an example of the internal voltage VDD is a bout 3 V,and an example of the boosted voltage VDDR is about 5 V.

As shown in FIG. 9, a detector 83 for detecting the level of the boostedvoltage VDDR may be arranged to keep the boosted voltage VDDR at apredetermined level (about 5 V in the second embodiment). The detector83 detects the level of the boosted voltage VDDR, and outputs a signalSVDDR for activating the booster 81 if the boosted voltage VDDR changeslower than the predetermined level, and deactivating it if the boostedvoltage VDDR changes higher than the predetermined level.

Al though the detector 83 need not always be arranged, it canparticularly prevent the boosted voltage VDDR from being lower than thepredetermined level. Accordingly, the situation wherein the boostedvoltage VDDR decreases to be closer to the threshold voltage Vthcell ofthe nonvolatile transistor 31 in an “ON” state can be avoided, and thereliability of the mode signal generator 16 further increases.

Third Embodiment

A read of data from the memory cell MC of the memory cell array 11 shownin FIGS. 8A to 8D does not start at the same time as power-on. This isbecause data is read out by inputting a read command to a powered chipand inputting an address.

To the contrary, a read of data from the nonvolatile transistor 31 ofthe mode signal generator 16 must start at the same time as power-on inorder to confirm the product type of powered chip.

A potential for outputting a signal PWON, i.e., a power-on detectionlevel is set lower than the assurance range of the power supply voltageto avoid a malfunction.

For example, in a product having a power supply voltage of about 3 V,the detection level is set to 2 V. The detection level of 2 V is equalto the threshold voltage (Vthcell=2 V) of the nonvolatile transistor 31in an “ON” state. In the product having the detection level of 2 V, ifthe power supply voltage does not reach 3 V but reaches 2 V, the signalPWON changes to “H” level. As a result, the 2-V signal PWON is suppliedto the gate of the nonvolatile transistor 31.

The threshold voltage Vthcell of the nonvolatile transistor 31 in an“ON” state is 2 V. At a gate voltage of 2 V, the nonvolatile transistor31 is kept off, so correct data cannot be read out.

Even in the use of the boosted voltage VDDR, like the second embodiment,if the internal voltage VDD does not reach 3 V, the booster 81 cannotgenerate any sufficiently boosted voltage VDDR. Accordingly, no correctdata may be read-out similar to the above case.

An object of the third embodiment is to correctly operate a mode signalgenerator 16 upon power-on.

For this purpose, in the third embodiment, a controller 82 operatesafter the boosted voltage VDDR reaches a satisfactory level.

FIG. 10 is a block diagram showing an example of the arrangement of asemiconductor integrated circuit device according to the thirdembodiment.

As shown in FIG. 10, the third embodiment employs a timing adjuster 84for delaying the rise of the signal PWON by a time required to changethe level of the external voltage VCC or internal voltage VDD to a setvoltage (e.g., 3 V). The operation of a booster 81 is enabled by asignal PWON′ from the timing adjuster 84. After the level of theinternal voltage VDD reaches the set voltage (e.g., 3 V), the booster 81operates to generate the boosted voltage VDDR.

The third embodiment further adopts a latch circuit (flip-flop) 85 resetby the signal PWON′ and set by the signal SVDDR. The latch circuit 85outputs a signal SVDDLAT representing that the level of the boostedvoltage VDDR reaches the set voltage (e.g., 5 V). The operation of thecontroller 82 is enabled by the signal SVDDLAT.

As described above, the operation of the controller 82 is enabled by thesignal SVDDLAT representing that the level of the boosted voltage VDDRreaches the set voltage (e.g., 5 V). With this setting, the controller82 operates after the boosted voltage VDDR reaches a satisfactory level.The “H” level of the signal FSWL can be set sufficiently higher than thelevel of the threshold voltage Vthcell of a nonvolatile transistor 31 inan “ON” state. Even if data is read out from the nonvolatile transistor31 at the same time as power-on of the chip, a read error in which thenonvolatile transistor 31 in an “ON” state is turned off can besuppressed, and the mode signal generator 16 can correctly operate uponpower-on.

Fourth Embodiment

A detailed circuit example of a semiconductor integrated circuit deviceto which the present invention is applied will be described as thefourth embodiment.

FIG. 11 is a flow chart showing an example of the control sequence of aflash EEPROM according to the fourth embodiment of the presentinvention. FIG. 12 is a block diagram of an example of the arrangementof the flash EEPROM according to the fourth embodiment of the presentinvention.

Detailed arrangements of circuits of respective blocks will besequentially explained below in accordance with the control sequence.

In step ST1 shown in FIG. 11, a chip is powered with the power supplyvoltage (external voltage VCC or the internal voltage VDD; in the fourthembodiment, the external voltage VCC is used). The level of the powersupply voltage VCC rises.

In step ST2, the level of the power supply voltage VCC is detected.Detection of the power supply voltage VCC is performed by a power-onreset circuit 101 shown in FIG. 12. The detection level of the powersupply voltage VCC must be matched by, of circuits arranged in the flashEEPROM, a circuit having the smallest margin VCCmin. In the fourthembodiment, the detection level of the power supply voltage VCC ismatched by a reference voltage generator 102 shown in FIG. 12.

FIG. 13 is a circuit diagram showing an example of the power-on resetcircuit 101.

In the power-on reset circuit 101 shown in FIG. 13, a low-pass filter201 made up of a capacitor C and a resistor R is connected to a powersupply terminal VCC in order to prevent a malfunction caused by anabrupt change in voltage VCC (power supply noise).

Diffusion resistors r1 and r2 in the power-on reset circuit 101 are ofan n-type in order to prevent a node having a low-speed internaloperation from being affected by noise. Each n-type diffusion resistoris formed in a p-type silicon substrate or well, and the p-typesubstrate or well is biased to the ground potential.

A diffusion resistor r3 series-connected between the power supplyterminal VCC and a diode D is of a p-type. The p-type diffusion resistoris formed in an n-type silicon substrate or well, and the n-typesubstrate or well is biased to, e.g., the voltage VCC.

When the power supply voltage VCC reaches the detection level, thepower-on reset circuit 101 outputs an “L”-level detection signal PONRST.The detection signal PONRST is equivalent to, e.g., the signal PWON inthe circuit shown in FIG. 10.

After the level of the power supply voltage VCC is detected, a referencevoltage VREF is generated in step ST3. The reference voltage VREF isgenerated by the reference generator 102.

FIG. 14 is a circuit diagram showing an example of the referencegenerator 102.

The reference generator 102 shown in FIG. 14 is a bandgap referencecircuit. In the bandgap reference circuit 102, natural transistors areused as N-channel MOS transistors N1 and N2 constituting a currentmirror circuit 202. A natural transistor has a threshold voltage ofabout 0 V, and can be formed by doping no impurity for adjusting thethreshold voltage in, e.g., a channel.

The lower limit of the operating voltage of the current mirror circuit202 shown in FIG. 14 is given by

VCCmin=VB(=VA)+VTHP

where VB is the forward voltage of a PN diode. VTHP is a thresholdvoltage of P-channel MOS transistor in the current mirror circuit 202.

This can be rewritten as

VCCmin=VF+VTHP

The power-on reset circuit 101 described with reference to FIG. 13 has avoltage detection level VPONRST given by

VPONRST=VF+VTHP

The voltage detection level VPONRST is matched with the lower limit ofthe operating voltage of the current mirror circuit 202 shown in FIG.14.

As described above, the bandgap reference circuit 102 generates thereference voltage VREF upon power-on. A capacitor C connected to theoutput node of the reference voltage VREF is a stabilized capacitor.

The bandgap reference circuit 102 operates even in a standby state inorder to keep the boosted voltage VDDR (to be described later) even in astandby state in the fourth embodiment. Considering demands for areduction in standby current, the current consumption must be suppressedto about several μA. To reduce the current consumption, the operationspeed of the bandgap reference circuit 102 shown in FIG. 14 is set verylow. For this reason, stabilization of the reference voltage VREFrequires several μs to several ten μs. Therefore, a series of operationswhich are to be performed inside the chip when the system is turned on,are not executed until the reference voltage VREF becomes stable afteran increase in the power supply voltage VCC is sensed. In the fourthembodiment, as shown in step ST4, timing adjustment up to generation ofa stable reference voltage VREF is performed parallel to step ST3.

FIG. 15 is a circuit diagram showing an example of a timing adjuster103.

The timing adjuster 103 shown in FIG. 15 adjusts the timing until thereference voltage VREF stabilizes after the detection signal PONRST isoutput. A CR time constant inside the timing adjuster 103 is set largerthan the time constant of the bandgap reference circuit 102.

In the timing adjuster 103 shown in FIG. 15, the CR time constant of afirst stage 203 is particularly set larger than the time constant of thebandgap reference circuit 102. The timing adjuster 103 outputs a signalBGRONRST representing the timing at which the reference voltage VREF issatisfactorily stabilized.

The signal BGRONRST is at “H” level for an “H”-level detection signalPONRST and at “L” level for an “L”-level detection signal PONRST. Uponthe lapse of a time determined by the CR time constant, the signalBGRONRST changes to “L” level.

After the reference voltage VREF stabilizes, the power supply voltageVCC is internally boosted in step ST5. Internal boosting is performed bya ring oscillator 104 for oscillating a driving pulse φP, and a chargepumping circuit 105 driven by the driving pulse φP.

FIG. 16 is a circuit diagram showing an example of the oscillator 104.FIG. 17 is a circuit diagram showing an example of the charge pumpingcircuit 105.

As shown in FIG. 16, the oscillator 104 is a circuit (ring oscillator)for logically oscillating an oscillation signal. The oscillator 104receives the signal BGRONRST, starts oscillating the driving pulse φP,and drives the charge pumping circuit 105 shown in FIG. 17.

As shown in FIG. 17, the charge pumping circuit 105 has capacitors foralternately receiving the driving pulse φP and an inverted driving pulse/φP, and boosts the power supply voltage VCC to the boosted voltageVDDR. An inactive/active state of the charge pumping circuit 105 isdetermined by disabling/enabling the oscillation operation of theoscillator 104.

To read out/latch data of a ROM corresponding to the nonvolatiletransistor 31 after internal boosting starts, the level of the boostedvoltage VDDR must be detected.

After internal boosting starts, the level of the boosted voltage VDDR isdetected in step ST6. The boosted voltage VDDR is detected by a VDDRlevel detector 106.

FIG. 18 is a circuit diagram showing an example of the VDDR leveldetector 106.

As shown in FIG. 18, the VDDR level detector 106 compares the referencevoltage VREF with a value obtained by dividing the boosted voltage VDDRby resistors. In the fifth embodiment, since internal boosting startsafter the reference voltage VREF is stabilized, the detector 106 shownin FIG. 18 outputs an “H”-level detection signal SVDDR when the boostedvoltage VDDR satisfies

VDDR={(R1+R2)/R2}·VREF

In the fourth embodiment, the detection signal SVDDR is fed back to theoscillator 104 to also be used as a signal for stopping the operation ofthe charge pumping circuit 105 and reducing the power consumption.

When a current flows through the boosted voltage VDDR within the chipupon operation to decrease the boosted voltage VDDR, the detectionsignal SVDDR changes to “L” level to operate the charge pumping circuit105. When the charge pumping circuit 105 operates, and the boostedvoltage VDDR reaches a satisfactory level again, the detection signalSVDDR changes to “H” level.

In this manner, the detection signal SVDDR alternately changes to “H”level and “L” level.

The detection signal SVDDR must be at “H” level to read out/latch dataof the ROM. However, data cannot be read out/latched every time thedetection signal SVDDR changes from “L” level to “H” level. This isbecause, during a chip operation, the latched data is in an unconfirmedstate, and the operation becomes unstable. Therefore, a signal forstarting the data read/latch sequence of the ROM (step ST7) when thedetection signal SVDDR changes to “H” level for the first time uponpower-on must be generated.

In the fourth embodiment, this signal is generated by a latch circuit107.

FIG. 19 is a circuit diagram showing an example of the latch circuit107.

The latch circuit 107 shown in FIG. 19 is a flip-flop reset by thesignal BGRONRST and set by the detection signal SVDDR. When thedetection signal SVDDR changes to “H” level for the first time, theflip-flop 107 outputs a signal SVDDRLAT latching “H”level. The signalSVDDRLAT starts the data read/latch sequence of the ROM.

FIG. 12 shows a circuit for embodying the data read/latch sequence ofthe ROM shown in step ST7.

In the fourth embodiment, the embodying circuit is constituted by a fusecell data latch trigger circuit 108, a fuse cell control circuit 109, afuse cell 110, and a fuse cell data latch circuit 111.

The fuse cell data latch trigger circuit 108 and the fuse cell controlcircuit 109 are equivalent to the controller 82, the fuse cell 110 tothe nonvolatile transistor 31, and the fuse cell data latch circuit 111to a circuit including the latch circuit 40. That is, the fuse cell 110and the fuse cell data latch circuit 111 are equivalent to the modesignal generator 16.

FIG. 20 is a circuit diagram showing an example of the fuse cell datalatch trigger circuit 108. FIG. 21 is a circuit diagram showing anexample of the fuse cell control circuit 109. FIG. 22 is a circuitdiagram showing an example of the fuse cell 110. FIG. 23 is a circuitdiagram showing an example of the fuse cell data latch circuit 111. FIG.24 is a waveform chart showing the operation of the data read/latchsequence.

As shown in FIG. 20, the fuse cell data latch trigger circuit 108receives the signal SVDDRLAT to generate a trigger signal TRIGGER. Thetrigger signal TRIGGER is at “H”level for a period corresponding to thedelay time of a delay circuit 204. When the trigger signal TRIGGERchanges to “H” level, the fuse cell data latch trigger circuit 108changes a signal FREAD to “H” level, and outputs it. The signal FREADkeeps “H” level for several ten ns (e.g., 50 ns) after the triggersignal TRIGGER changes to “L” level. The “H”-level duration is set by adelay circuit 207 obtained by alternately connecting inverters 205 eachhaving a capacitor Cc at an output node, and inverters 206 each having acapacitor Cd at an output node.

The capacitor Cc is charged by the trigger signal TRIGGER, and thecapacitor Cd is discharged by the trigger signal TRIGGER. After thetrigger signal TRIGGER changes to “L”level, the capacitor Cc discharges.Upon the discharge, an input level to an inverter 206 on the outputstage is inverted. Upon the inversion, the capacitor Cd of the inverter206 is charged.

As shown in FIG. 21, the fuse cell control circuit 109 outputs an“H”-level signal FSREAD while the signal FREAD is at “H” level. The fusecell control circuit 109 outputs signals FSBIAS and FSWL which change to“H” level after the signal FREAD changes to “H” level. The signalsFSBIAS and FSWL keep “H” level for a short time (e.g., 10 ns) even afterthe signal FREAD changes to “L” level.

As shown in FIG. 22, the fuse cell 110 has a nonvolatile memory cell MC(corresponding to the nonvolatile transistor 31). The signal FSWL isinput to the control gate of the memory cell MC, and its level is theboosted voltage VDDR.

The fuse cell 110 has an N-channel MOS transistor N3 (corresponding tothe transistor 32) series-connected to a bit line FBL of the memory cellMC. The transistor N3 is made up of a natural transistor, and itsthreshold voltage is about 0 V. The signal FSBIAS is input to the gateof the transistor N3, and its level is the external voltage VCC lowerthan the boosted voltage VDDR (or the internal voltage VDD lower thanthe boosted voltage VDDR).

As shown in FIG. 23, the fuse cell data latch circuit 111 has P-channelMOS transistors P1 and P2 series-connected between a power supplyterminal VCC and the bit line FBL. An inverted signal /FSREAD of thesignal FSREAD is input to the gates of the transistors P1 and P2. Thetransistors P1 and P2 constitute the load 34. When the signal FSREAD isat “H” level, data FUSEBIT read from the memory cell MC is determined bythe amount of currents flowed by the load 34, particularly thetransistor P1 and the memory cell MC. The data FUSEBIT is latched by thelatch circuit 40. When the signal FSREAD changes to “L” level, the latchcircuit 40 is completely disconnected from the fuse cell 110 to confirmthe data. The latch circuit 40 outputs a signal FUSE in accordance withthe latched contents. The signal FUSE is equivalent to the signal MODE.

After the data is confirmed, the control gate of the memory cell MC isgrounded, the transistors P1 and P2 of the load 34, and a switch 37 areturned off. Accordingly, the memory cell MC can be set in a read statefor only a short time upon power-on. No extra read stress (electricalstress) is applied to the memory cell MC upon the completion of the dataread/latch sequence of the ROM.

Subsequently, if the chip is in a non-selected state, the flow shifts toa standby mode in step ST8; if the chip is in a selected state, the flowshifts to, e.g., a read mode in step ST9.

In the flash EEPROM according to the fourth embodiment, the dataread/latch sequence of the ROM starts after the reference voltage VREFsatisfactorily stabilizes. For this reason, a satisfactorily stableboosted voltage VDDR can be applied to the gate of the memory cell MC ofthe fuse cell 110. A data read error and the like can be suppressed, andcorrect data can be latched by the latch circuit 40 of the fuse celldata latch circuit 111.

After the data of the latch circuit 40 is confirmed, the control gate ofthe memory cell MC of the fuse cell 110 is grounded to decrease thepotential difference between the control gate and the substrate tosubstantially 0. With this setting, the memory cell MC of the fuse cell110 becomes free from any electrical stress except for only a short timeupon power-on. The electrical stress applied to the memory cell MC ofthe fuse cell 110 is smaller than, e.g., that applied to the memory cellMC of the memory cell array 11. The progress of a deterioration inmemory cell MC of the fuse cell 110 is suppressed, compared to that ofthe memory cell MC of the memory cell array 11. This reduces thepossibility of occurrence of the situation wherein the fuse cell 110breaks before the memory cell array 11. Therefore, the reliability ofthe fuse cell 110 increases.

After the data of the latch circuit 40 is confirmed, the load 34 isturned off. With this arrangement, the potential difference between thesource and drain of the memory cell MC of the fuse cell 110 is decreasedto substantially 0. An electrical stress applied to the memory cell MCof the fuse cell 110 can be suppressed, and the reliability of the fusecell 110 can be increased.

Further, after the data of the latch circuit 40 is confirmed, the switch37 between the latch circuit 40 and the fuse cell 110 is turned off.With this arrangement, even if the latch circuit 40 latches data whichchanges a node on the fuse cell 110 side to “H” level, the potentialdifference between the source and drain of the memory cell MC of thefuse cell 110 can be decreased to substantially 0. Consequently, anelectrical stress applied to the memory cell MC of the fuse cell 110 canbe suppressed, and the reliability of the fuse cell 110 can beincreased.

After the data is confirmed, the control gate of the memory cell MC ofthe fuse cell 110 is grounded, and the transistors P1 and P2 of the load34 are turned off. This suppresses unwanted power consumption to realizesmall power consumption.

Fifth Embodiment

The fifth embodiment is directed to input of a chip enable signal /CEfor selecting a chip during the data read/latch sequence of the ROMafter power-on.

Input of the signal /CE during the data read/latch sequence of the ROMmay cause a malfunction because latched data is not confirmed.

For this reason, a signal FEND representing the end of the dataread/latch sequence is generated within the chip. This signal FEND isoutput from a fuse cell data latch trigger circuit 108′ in the fifthembodiment.

FIG. 25 is a circuit diagram showing an example of the fuse cell datalatch trigger circuit 108′ according to the fifth embodiment. FIG. 26 isa waveform chart showing the operation of a data read/latch sequenceaccording to the fifth embodiment.

As shown in FIGS. 25 and 26, after a signal FREAD changes to “L” level,the signal FEND changes to “H” level upon the lapse of a delay time setby a delay circuit 301. The signal FEND keeps “H” level during a delaytime set by a delay circuit 302.

FIG. 27A is a view showing the layout of flash EEPROMs on a circuitboard according to the fifth embodiment.

As shown in FIG. 27A, the fifth embodiment employs internal chip enablesignal output circuits 112. The internal chip enable signal outputcircuits 112 generate internal chip enable signals ICEINT upon receptionof chip enable signals /CE (/CE1 to /CEn) externally supplied, and thesignal END internally generated.

FIG. 27B is a circuit diagram showing an example of each internal chipenable signal output circuit 112.

As shown in FIG. 27B, the internal chip enable signal output circuit 112has a flip-flop 303 reset by a detection signal PONRST and set by thesignal FEND.

The internal chip enable signal /CEINT is generated based on the ORbetween an output from the flip-flop 303 and the chip enable signal /CE.

In the flash EEPROM according to the fifth embodiment, a disabled stateis held for an external chip access request during the data read/latchsequence of the ROM. This disabled state is canceled upon completion ofthe sequence.

In the fifth embodiment, a standby state is kept until the internal chipenable signal /CEINT is output even if the chip enable signal /CE isinput. After the signal FEND is output to represent the end of the dataread/latch sequence of the ROM, the chip is set in a selected state.

As a result, even if the chip enable signal /CE is input during the dataread/latch sequence of the ROM, the device can be prevented fromoperation errors.

Sixth Embodiment)

The sixth embodiment concerns reset of the fuse cell data latch triggercircuit 108 upon power-on.

FIG. 28 is a circuit diagram showing an example of a fuse cell datalatch trigger circuit 108″ according to the sixth embodiment.

As shown in FIG. 28, the fuse cell data latch trigger circuit 108″comprises N-channel MOS transistors N4 respectively for resetting asubstantial output node 401 of a signal FREAD, a substantial output node402 of a signal FEND, and a delay circuit 207 by using a detectionsignal PONRST or signal BGRONRST.

In this way, the fuse cell data latch trigger circuit 108″ can be resetusing the detection signal PONRST or signal BGRONRST.

Seventh Embodiment

The seventh embodiment is about the arrangement of a fuse cell 110 on achip.

One data FUSEBIT requires only one memory cell MC constituting the fusecell 110, and thus only one word line is necessary. That is, a word lineand a plurality of bit lines crossing the word line are formed, and aplurality of memory cells MC each having a floating gate FG are formedin a line at electrical intersections of the word line and the bitlines.

Today, however, with the advance of micro-patterning, it is verydifficult to form only one word line (control gate) for the memory cellsMC on a chip.

More specifically, in a technique of forming word lines by resistpatterning, the reproducibility of a pattern having only one isolatedfine word line is very poor. If no word line can be reproduced on aboard with a design size, the characteristics of the memory cells MC mayfall outside design values, and no correct data can be written/read out.This results in low reliability of the fuse cell 110.

An object of the seventh embodiment is to keep high reliability of thefuse cell 110 even when the fuse cell 110 is micro-patterned.

For this purpose, in the seventh embodiment, dummy patterns are arrangedin an array (to be referred to as a fuse cell array hereinafter) whereinfuse cells 110 are aligned. A normal pattern in which the fuse cells 110are aligned is sandwiched between the dummy patterns.

FIG. 29 is a plan view of the pattern of a fuse cell array according tothe seventh embodiment. FIG. 30 is an equivalent circuit diagram of thefuse cell array.

As shown in FIGS. 29 and 30, a plurality of word lines WL and aplurality of bit lines FUSEBIT crossing these word lines WL are formedin a fuse cell array 114. The memory cells MC are formed at electricalinter-sections of the word lines WL and the bit lines FUSEBIT, andarrayed in a matrix in the fuse cell array 114.

In the fuse cell array 114 according to the seventh embodiment, six wordlines WL1 to WL6 are formed. Of these word lines WL1 to WL6, the wordline WL4 laid out at almost the center serves as a word line for normalmemory cells MC. A signal FSWL is supplied to the word line WL4 for thenormal memory cells MC. All the remaining word lines WL1 to WL3, WL5,and WL6 are dummy pattern word lines DPWL (DPWL1 to DPWL3, DPWL5, andDPWL6). For example, the dummy pattern word lines DPWL are alwaysgrounded.

A source line SL for the memory cells MC is formed by a self-alignedsource technique (SAS TEC.) using the word lines WL as a mask.

Three source lines SL are formed in the fuse cell array 114 according tothe seventh embodiment. Of the three source lines SL, a central sourceline SL serves as a source line for the normal memory cells MC. A signalFSVS is supplied to the source line SL for the normal memory cells MC.The voltage of the signal FSVS changes depending on a write/read/erasemode. All the remaining source lines are dummy pattern source linesDPSL, and, e.g., float.

Of memory cells MCl-to MC6 aligned along the bit lines FUSEBIT, thememory cells MC4 are normal memory cells MC. All the remaining memorycells MC1 to MC3, MC5, and MC6 are dummy pattern memory cells DPMC(DPMC1 to DPMC3, DPMC5, and DPMC6). The normal memory cells MC4 areelectrically connected to the bit lines FUSEBIT via fuse bit contacts501.

In the fuse cell array 114 according to the seventh embodiment, eachfuse bit contact 501 is shared by adjacent memory cells MC. Each normalmemory cell MC4 shares the fuse bit contact 501 with the dummy patternmemory cell DPMC5. However, no dummy pattern memory cell DPMC5 isselected because the word line DPWL5 for the dummy pattern memory cellDPMC5 is grounded.

One end of each of the bit lines FUSEBIT1 to FUSEBIT8 is connected to alatch circuit 111, and the other end is connected to a fuse cell dataprogram circuit 115. The fuse cell data program circuit 115 is used inwriting data in the memory cell MC.

As described above, the dummy patterns are formed in the fuse cell array114, and the normal word line WL is sandwiched between the dummy patternword lines DPWL. Even the normal word line WL which should be originallyisolated can be faithfully reproduced on a board with a design size.Consequently, the characteristics of the normal memory cells MC can beprevented from falling outside design values. Correct data can bewritten/ read out, and the reliability of the fuse cell 110 increases.

Eighth Embodiment

The eighth embodiment is about the type of data stored in a fuse cell110.

As described in the first embodiment, various types of data stored inthe fuse cell 110 are conceivable. Typical examples of the data are

(a) redundancy data for activating/deactivating a redundancy defectiveaddress and a spare decoder,

(b) data representing the address of a write/erase inhibit block,

(c) bit configuration setting data for determining the number of bits ofI/O data,

(d) switching data for a pad location corresponding to a package,

(e) TOP BOOT/BOTTOM BOOT switching data for determining the size of ablock subjected to a data erase, and

(f) data for deactivating (inhibiting the use of) an internal testcircuit represented by, e.g., a built-in test circuit used to test achip.

In the fuse cell 110, these pieces of chip operation/function settinginformation are stored, and the operation and function of the chip areset in accordance with these operation/function setting information.

FIG. 31 is an equivalent circuit diagram of a fuse cell array accordingto the eighth embodiment.

In a conventional concept, data (a) to (f) are set by the manufacturer.Data (a) to (f) are stored in a read-only ROM by a fuse or bondingoption method.

In a flash EEPROM described in the first to seventh embodiments, awritable ROM is used for a memory cell of the main body, so that thememory cell MC of the fuse cell 110 can be made up of a writable ROM.Accordingly, data can be rewritten.

As shown in FIG. 31, in the ninth embodiment, to allow rewrite of data(a) to (f), a fuse cell data program/erase circuit 115′ is connected tobit lines FUSEBIT of memory cells MC.

According to the ninth embodiment, not only the manufacturer but alsothe user can switch, of data (a) to (f), for example,

(b) data representing the address of a write/erase inhibit block,

(c) bit configuration setting data for determining the number of bits ofI/O data, and

(e) TOP BOOT/BOTTOM BOOT switching data for determining the size of ablock subjected to a data erase. By allowing the user to switch data(b), (c), and (e), a product convenient for the user can be provided.

Ninth Embodiment

The ninth embodiment is about the layout of a fuse cell array 114 on achip.

FIG. 32 is a block diagram showing an example of the arrangement of aflash EEPROM according to the ninth embodiment.

As shown in FIG. 32, some fuse cells 110 are grouped into one fuse cellarray 114, and collectively laid out at a given portion.

By grouping the fuse cells 110 into one fuse cell array 114, andcollectively laying them out, the fuse cells 110 can be efficiently laidout on the chip, and particularly an increase in chip area can besuppressed.

The fuse cell array 114 is arranged near a fuse cell data latch circuit111 in the ninth embodiment.

Tenth Embodiment

The tenth embodiment exemplifies the formation direction of a word lineWL formed on a fuse cell array 114.

FIG. 33 is a view showing the relationship between the fuse cell arrayof a flash EEPROM according to the tenth embodiment, and a main memorycell array.

As shown in FIG. 33, the fuse cell array 114 and a main memory cellarray 11 are formed on one chip 601. In the fuse cell array 114 and themain memory cell array 11, a plurality of word lines WL, and a pluralityof bit lines (not shown) crossing these word lines WL are formed. Aplurality of memory cells each having a floating gate FG are formed atelectrical intersections of the word lines WL and the bit lines.

In the fuse cell array 114 and the main memory cell array 11, thedirection of the word line WL formed on the fuse cell array 114preferably coincides with the direction of the word line WL formed onthe main memory cell array 11.

If the directions of the word lines WL do not coincide with each other,the characteristics of a memory cell formed in the fuse cell array 114may be greatly different from those of a memory cell formed in the mainmemory cell array 11 due to a problem in process. The difference incharacteristics makes it difficult to read out data using the sameboosted voltage VDDR with high reliability.

The problem in process is, e.g., a “shadow effect”. The source and drainregions of a memory cell are formed by “ion”-implanting an impurityserving as the donor/accepter of a semiconductor by using the word linesWL as a mask. In general, these “ions” are implanted obliquely at apredetermined angle with respect to a semiconductor substrate such as asilicon wafer. In this implantation, the impurity implanted in thesource and drain regions is shielded by the word lines WL, and theconcentration differs between the source and drain regions. This is aso-called “shadow effect”. The difference in concentration between thesource and drain regions changes the characteristics of the memory cell.

In the tenth embodiment, to solve this problem, the word line WL in thefuse cell array 114 is formed in the same direction as that of the wordline WL formed in the main memory cell array 11.

More specifically, by making the formation directions of the word linesWL in the fuse cell array 114 and the main memory cell array 11 coincidewith each other, e.g., the source/drain region of a memory cell formedin the fuse cell array 114, and that of a memory cell in the main memorycell array 11 can be formed under the same conditions. As a result, boththe memory cells can have the same characteristics.

If the memory cells formed in the fuse cell array 114 and the mainmemory cell array 11 have the same characteristics, data can be read outfrom the fuse cell array 114 and the main memory cell array 11 using,e.g., the same boosted voltage VDDR with high reliability.

If data can be read out from the fuse cell array 114 and the main memorycell array 11 using, e.g., the same boosted voltage VDDR, the fuse cellarray 114 and the main memory cell array 11 can share a generator forgenerating the boosted voltage VDDR, e.g., in the first to ninthembodiments, a circuit portion made up of the ring oscillator 104, thecharge pumping circuit 105, the VDDR level detector 106, and the like.

Sharing the circuit portion for generating the boosted voltage VDDR bythe fuse cell array 114 and the main memory cell array 11 can suppressan increase in chip area. Particularly, a capacitor included in thecharge pumping circuit 105 requires a large area. An increase in chiparea can be greatly suppressed by sharing the circuit including thecharge pumping circuit 105, i.e., the booster 81 by the fuse cell array114 and the main memory cell array 11.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A detecting circuit formed on a semiconductorsubstrate with a fixed potential point and a variable potential pointhaving a potential difference from the fixed potential point thatchanges upon power-on, to detect that the potential difference betweenthe fixed potential point and the variable potential point reaches apredetermined potential difference, comprising: a first resistorconnected to the variable potential point; and a second resistor notconnected to the variable potential point, and wherein said firstresistor is formed in a first semiconductor region biased to a potentialof the variable potential point, and said second resistor is formed in asecond semiconductor region biased to a potential of the fixed potentialpoint.
 2. A circuit according to claim 1, wherein the fixed potential isa ground potential, said first resistor is a p-type diffusion resistorformed in an n-type semiconductor region, and said second resistor is ann-type diffusion resistor formed in a p-type semiconductor region.
 3. Adetecting circuit for detecting a power-on potential level, saiddetecting circuit being formed on a semiconductor substrate with a fixedpotential point and a variable potential point having a potentialdifference from the fixed potential point that changes upon power-on, todetect that the potential difference between the fixed potential pointand the variable potential point reaches the power-on potential level,comprising: a first resistor connected to the variable potential point;and a second resistor not connected to the variable potential point, andwherein said first resistor is formed in a first semiconductor regionbiased to a potential of the variable potential point, and said secondresistor is formed in a second semiconductor region biased to apotential of the fixed potential point.
 4. The circuit according toclaim 3, wherein the fixed potential is a ground potential, said firstresistor is a p-type diffusion resistor formed in a n-type semiconductorregion, and said second resistor is an n-type diffusion resistor formedin a p-type semiconductor region.
 5. The circuit according to claim 4,wherein the variable potential is a power supply potential.
 6. Thecircuit according to claim 5, wherein the n-type semiconductor region isbiased to the power supply potential, and the p-type semiconductorregion is biased to the ground potential.
 7. The circuit according toclaim 3, further comprising: a low pass filter coupled between thevariable potential point and a power supply terminal.
 8. The circuitaccording to claim 7, wherein the fixed potential is a ground potential,said first resistor is a p-type diffusion resistor formed in an n-typesemiconductor region, and said second resistor is an n-type diffusionresistor formed in a p-type semiconductor region.
 9. The circuitaccording to claim 8, wherein the variable potential is a power supplypotential.
 10. The circuit according to claim 9, wherein the n-typesemiconductor region is biased t the power supply potential, and thep-type semiconductor region is biased to the ground potential.